1. Field of the Invention
This invention relates to a II-VI compound semiconductor based red-green or -blue light emitting device.
2. Description of the Related Art
As described in "Applied Physics Letters, 63, 3107(1993)", the degradation of a wide-gap II-VI compound semiconductor based light emitting device occurs by the stacking faults or through dislocations formed during crystal growth. The letter reveals that rapid formation and propagation of such defects occur in the active layer at relatively high current densities required for lasing, leading to the formation of a dislocation network.
As described in "Applied Physics Letters, 65, 801(1994)", dark line defects in the &lt;100&gt; direction are observed in or in the vicinity of the active layer of the II-VI compound semiconductor based light emitting device which have been degraded by the application of a current, and point defects are presumed to participate in the dark line defects.
Stacking faults generated from the crystal interface between a GaAs substrate and a II-VI compound, which are regarded to be a cause for the degradation, can be suppressed to 1.times.10.sup.4 /cm.sup.2 or lower by forming a GaAs buffer layer on the GaAs substrate to cover the substrate with As and then exposing the resulting substrate to Zn ["Applied Physics Letters, 68, 2413(1966)"].
Even if the crystal defects appearing from the interface can be reduced, the formation and propagation of defects in the active layer which are formed at the time when a current is applied cannot be avoided. The existing II-VI compound semiconductor based laser is accompanied with the drawbacks such as a short lifetime, as short as about 100 hours, and difficulty in mass production from the viewpoints of reproducibility and reliability [Taniguchi et al., "Electronics Letters, 32, 552(1996)].